High-speed digital copiers are widely available and their use in mid-size offices or as departmental printers/copiers is becoming commonplace. In addition to printing and copying functions, it is known that facsimile and/or digital scanning for copying, printing, faxing and/or disk storage (locally or networked computer) can be provided in a single unit. Such devices may be encompassed by the term “printer”, and are also known as “digital copier”, “multifunction” or “multimode” machines.
The speed at which digital copiers are capable of generating and printing images on output media is continually increasing. However, when considering the overall performance or throughput of a device, the rate at which these devices are capable of printing images on output media is only one factor to consider. In addition, one should also consider the speed at which information from hardcopy original documents is captured and processed. The rate at which digital copiers capture and process information from hardcopy documents is typically slower than the rate at which they can print pages. Thus, when performing copying or scanning operations, many such devices are limited by the speed at which information from hardcopy documents is captured and processed.
Briefly reviewing, digital copiers typically use a constant velocity transport (CVT) document feeding system or similar feeding device when capturing or scanning information from hardcopy documents. It is known that CVT type scanning devices can provide rapid and closely spaced document exchange times at the imaging station to obtain document feeding and scanning at greater than 50 scanned documents per minute. In addition, CVT type scanning devices can be used with a variety or mixture of document sizes, types, weights, thickness and materials as well as documents which may have curls, wrinkles, tears, “dog-ears”, cut-outs, overlays, tape, paste-ups, punched holes, staples, adhesive or slippery areas, or other irregularities. Merely by way of one example, a complete description of CVT document feeding system is described and shown in U.S. Pat. No. 5,488,464, issued Jan. 30, 1996 to Steven J. Wenthe, Jr., et al. and incorporated herein by reference.
As has been described in the prior art, a common method for duplex scanning an input document with a CVT type scanning device includes scanning or imaging a first (simplex) side at an exposure station; using an inversion mechanism to invert and reverse the path of the input document; bringing the second (duplex) side into the same exposure station; and scanning or capturing the second side at the exposure station. See, for example, U.S. Pat. No. 4,419,007. Such inversion, however, requires sheet movement changes and additional mechanisms to start and stop the inversion mechanism. The change in direction and the additional mechanisms required to implement such change may create losses in productivity, reduce throughput, increase the possibility of document jams, and increase the number of components.
Duplex document scanning systems which can capture image data from both sides of a document as the document is moved along a continuous, non-inversion path are also well known. Such duplex scanning systems include two separate imaging stations, one for each of the two sides of the duplex document, along the document path. As a document traverses the path, each side of the document is imaged with a scanning element such as a raster input scanner (RIS). The RIS may be, for example, a full width array (FWA) type, or a CCD array or chip with lens image reduction. Duplex document scanning systems provide increased speed at the expense of increased hardware and software complexity and increased system resource requirements (e.g., memory, components, etc.). Examples of such duplex scanning systems can be found in U.S. Pat. Nos. 4,743,974 (Lockwood), 5,463,451 (Acquaviva et al.) and 5,680,204 (Ferrara), the teachings of each being incorporated herein by reference.